Pulmonary Embolism is at present a highly prevalent and frequently lethal disease (present in greater than 10% of autopsied cases) which is undiagnosed clinically in more than 50 percent of cases, and for which rational and frequently effective therapy is available. While lung scanning and pulmonary arteriography are good diagnostic procedures, neither is fully effective, and they are generally too complex as screening procedures. Present screening procedures lack specificity and reliability. It is therefore planned to develop a simple chemical screening procedure for pulmonary embolism which would have more specificity and accuracy than presently available methods. Lung and serum biochemistry will be studied and correlation sought between the serum concentration of a chemical constituent derived from lung and the presence of pulmonary embolism. It is thus anticipated that this research will contribute to the advancement of pulmonary embolism diagnosis as well as of knowledge of biochemistry of the lung which has been relatively little studied, and which may have implications for other pulmonary disease as well.